The diesel emissions cheating scandal will cost Volkswagen an extra $3bn (€2.5bn), because engines are proving "far more technically complex and time consuming" to adapt the company said, reports BBC.
Two years after the problems first emerged, Volkswagen is still struggling to put the crisis behind it.
The additional cost, for fixing engines in the United States, takes the total bill for the scandal to $30bn.
Shares in the German carmaker initially fell sharply, before recovering ground.
"This is yet another unexpected and unwelcome announcement from VW, not only from an earnings and cash flow perspective but also with respect to the credibility of management," said Arndt Ellinghorst, analyst at Evercore ISI.
VW first admitted in September 2015 that it had used illegal software to cheat US emissions tests.
Since then the firm has been adapting its cars to meet legal requirements. But the process in the United States is proving tougher than expected.
It is also amending cars in Europe, but the process there is more straightforward, VW said.
The additional costs will be reflected in VW's third quarter results, which will be reported next month.